TWI646760B - Electric conversion device - Google Patents

Abstract

An electric conversion device includes a bridge rectifier 10 having an input side and an output side, and a switched capacitor line 16 provided in parallel with the output side of the bridge rectifier. The switched capacitor line 16 includes A capacitor 18 and a switch 20 can control the charging and discharging of the capacitor 18. The invention also discloses an electric conversion method. When the output voltage of the bridge rectifier is higher than the threshold level 26 and continues to rise, the switch is closed to charge the capacitor and the output voltage of the bridge rectifier meets a load. When the output voltage is higher than the threshold level 26 and gradually decreases, disconnect the switch to isolate the capacitor from the load, and the output voltage of the bridge rectifier still meets the load; and when the output voltage of the bridge rectifier is lower than the threshold level 26 , Close the switch, so that the discharge of the capacitor is supplied to the load. The threshold level 26 may be dynamically controlled, such as responding to the output of a monitoring circuit 32.

Description

Electric conversion device

The present invention relates to a device and method for electrical conversion, for example, for converting AC power to DC power.

Rectification configurations for converting DC power to AC power are well known. This configuration typically includes a diode network configured as a bridge rectifier that is operable to convert an input AC voltage to a pulsed DC voltage, and its magnitude will vary with the input voltage. And it keeps changing. In order to eliminate some changes in the magnitude of the output voltage, it is common practice to provide a smoothing capacitor in parallel with the bridge rectifier. This type of capacitor not only requires a high capacitance value, usually several thousand microfarads, but also has a large actual size.

Although the operation of this rectifier configuration is satisfactory, problems often occur when the power supply to the associated load must be switched, especially in medium and high power applications. Furthermore, the need to integrate circuits in order to suppress harmonics is also a problem. In addition, the power factor of such a configuration tends to be low, typically around 0.3 to 0.6.

An object of the present invention is to provide an electric conversion device and method, which can overcome many of the disadvantages associated with the conventional electric conversion technology or reduce the effects of these disadvantages.

According to a first aspect of the present invention, an electric conversion device is provided. An input side and an output side bridge rectifier, and a switched capacitor line arranged in parallel with the output side of the bridge rectifier. The switched capacitor circuit includes a capacitor and a switch connected in series, so that the switch can control the charging and discharging of the capacitor.

The switched capacitor circuit may further include an inductor as needed. However, this is not necessary.

The switch preferably includes a bidirectional switch, for example, a pair of unidirectional switches arranged in parallel and opposite directions.

The invention further relates to a method for electrical conversion, which includes providing a switched capacitor line provided in parallel with an output side of a bridge rectifier. The switched capacitor line includes a capacitor and a switch connected in series, so that the switch Can control the charging and discharging of the capacitor. When the output voltage of the bridge rectifier is higher than a threshold level and continues to rise, the switch is closed to charge the capacitor and the output voltage of the bridge rectifier meets a load. ; When the output voltage of the bridge rectifier is higher than the threshold level and the voltage gradually decreases, turn off the switch to isolate the capacitor from the load, and the output voltage of the bridge rectifier still meets the load; and When the output voltage is lower than the threshold level, the switch is closed, so that the discharge of the capacitor is supplied to the load.

The switch includes a pair of unidirectional switches arranged in parallel and opposite directions, for example, a diode that controls the direction of the current. It should be understood that when performing the overall operation in the above manner, each switch need not always occupy the same position of another switch. For example, each unidirectional switch may include a suitable switching device such as, but not limited to, a metal oxide semiconductor field effect transistor (MOSFET) or an insulated gate bipolar transistor (IGBT).

An advantage of the aforementioned conversion device and method over a general conversion device is that the power factor associated with its operation has increased significantly. For example, this power factor It can be a level of 0.895. However, this is only an example of the power factor, not the upper limit of the achievable power factor.

The capacitance may be much smaller than the smoothing capacitance of a general conversion device. For example, the size of the capacitor may be as low as 10% of the size of a general smoothing capacitor. Therefore, compared with the general configuration, the present invention can save the cost of components and reduce the size of components.

Another advantage of the device and method of the present invention is that the harmonics generated in the current waveform are relatively low. Therefore, for an electrical or electronic device, since the present invention does not require an integrated circuit to adapt or remove such harmonics in terms of power supply conversion, it is relatively simple to adopt the device and method of the present invention.

The operation of the switch can be manipulated using any suitable control configuration. When the operation of this switch is synchronized with the output of the bridge rectifier, and the output of the rectifier is further synchronized with the input of the bridge rectifier, the operation of this switch can be synchronized with the input or output of the bridge rectifier. Alternatively, the output voltage from the bridge rectifier can be monitored or compared with a threshold level to determine the required switch position, and the position of the switch can be adjusted accordingly.

The switch usually needs to be able to be switched at a high potential. As described above, when the output from the bridge rectifier reaches its peak, the switch is turned off to terminate the charging of the capacitor and maintain the charge in the capacitor. When the charge in the capacitor becomes high, the switch is closed immediately, so that the capacitor satisfies the load.

10‧‧‧Bridge Rectifier

10a‧‧‧input side

10b‧‧‧Output side

12‧‧‧ Power

14‧‧‧ smoothing capacitor

16‧‧‧Switched Capacitor Circuit

18‧‧‧ switched capacitor (capacitance)

20‧‧‧Switch

20a, 20b ‧‧‧ one-way switch

22‧‧‧Control Configuration

24‧‧‧Output voltage

26‧‧‧ threshold level

28‧‧‧Load (resistance)

30‧‧‧Output voltage

32‧‧‧ monitoring circuit

34‧‧‧Inductance

36‧‧‧flywheel diode

38‧‧‧Switch

40‧‧‧DC-DC converter

The present invention will be further described in detail through embodiments and with reference to the accompanying drawings, in which: FIG. 1 is a circuit diagram of a general electric conversion device; FIG. 2 is a waveform diagram for assisting in understanding the circuit operation of FIG. 1; The embodiment is a circuit diagram of an electric conversion device; Fig. 4a is a schematic diagram of the theoretical output voltage of the electric conversion device of Fig. 3; Fig. 4b is a diagram of the actual output voltage of the electric conversion device of Fig. 3; Equivalent operating circuit; Figure 6a is a schematic diagram of the theoretical impact of harmonics on input current; Figure 6b is a test result chart showing the actual impact of harmonics on input current; Figure 7 is a comparison of test results showing three different circuit configurations Figure 7a shows the test results of the actual input current harmonics of the electrical device of Figure 1 with a 660μF smoothing capacitor 14 and a 36Ω load 28; Figure 7b shows Figure 3 with a 660μF switched capacitor 18 and a 36Ω load 28 Test results of actual input current harmonics of the electric device of FIG. 7; and FIG. 7c shows test results of actual input current harmonics of the electric device of FIG. 3 with 68 μF switched capacitor 18 and 36Ω load 28; A circuit diagram of an electric conversion device according to an embodiment; FIG. 9 is a circuit diagram of an electric conversion device according to another embodiment of the present invention; FIG. 10 is a series of circuit diagrams showing Individual equivalent operating circuits for the three operating modes of the device; FIG. 11 is a schematic diagram of the theoretical output voltage of the electric conversion device of FIG. 9, showing the effect of an additional storage element 34 on the voltage of mode 3; FIG. 13 is a circuit diagram of an electric conversion device according to still another embodiment of the present invention; and FIG. 14 shows an actual input current of the electric device of FIG. 1 relative to the electric device of FIG. 13. Comparison of test results of wave; Figure 14a shows the input current harmonic test results of the electrical device of Figure 1 with a DC-DC converter connected to the output side and provides a resistive load; and Figure 14b shows Figure with the same load as Figure 8a The test result of the input current harmonics of the electric device of 13.

Referring first to FIG. 1, a conventional AC / DC power conversion circuit configuration is shown. The aforementioned configuration includes a bridge rectifier 10 composed of a diode network (or a plurality of switches with a control device), and the AC power source 12 provides an input voltage to the rectifier 10 in a conventional manner. Figure 2a shows schematically that the output of the AC power source 12 is applied to the input side 10a of the bridge rectifier 10, and Figure 2b shows the output of the bridge rectifier in response to this input (without any smoothing). The bridge rectifier 10 is thus used to convert the AC power source 12 into DC outputs of different sizes.

In order to make the DC output of the bridge rectifier 10 better, a smoothing capacitor 14 is usually provided in parallel with the output side 10 b of the bridge rectifier 10. The capacitance of the smoothing capacitor 14 is usually large. The smoothing capacitor 14 is charged and discharged, thereby smoothing the output signal into a form as shown in FIG. 2c. It should be understood that although the output of the conversion circuit including the smoothing capacitor 14 is in the form of a DC output, there is still a significant output ripple, and its size is determined to some extent by the smoothing capacitor 14.

Electrical conversion using this general form circuit has been used for many years. One disadvantage of using such circuits is the low power factor of the circuit, which is typically around 0.3 to 0.6, for example. In addition, the presence of the large smoothing capacitor 14 causes large current harmonics to be generated in the power supply. If there is no compensation or suppression, it will interfere with the operation of other circuits.

The electrical conversion circuit configuration according to an embodiment of the present invention is shown in FIG. 3. At first glance, the circuit of FIG. 3 is very similar to the circuit of FIG. 1. However, there is an important difference between them. Specifically, the large smoothing capacitor 14 in the configuration of FIG. 1 is omitted and replaced with a switched capacitor circuit 16. The switched capacitor circuit 16 incorporates a capacitor 18 that is much smaller than a conventional smoothing capacitor 14. For example, the electricity displayed on the configuration The capacity 18 value is less than 100 μF. However, it should be understood that the present invention is not limited thereto, and it can use components with other capacitance values. In addition, the electrical conversion circuit configuration of the present invention includes a bidirectional switch 20. The switch 20 is operable to control the timing of charging and discharging the capacitor 18.

As is known to all, the large smoothing capacitor 14 existing in the conventional electric conversion circuit can cause significant current harmonics, which will have a negative impact on the operation of other circuits or devices, and therefore needs to be removed. By avoiding such capacitors, the generation of current harmonics is significantly reduced.

Since the switch 20 can control charging and discharging, the switch 20 is preferably a bidirectional switch. In the illustrated configuration, the bidirectional switch includes a pair of unidirectional switch pins in opposite directions, each of the unidirectional switch pins including a unidirectional switch 20a, 20b and a suitably positioned diode or similar element. A control configuration 22 is used to control the operation of the switch 20, control the position of each of the one-way switches 20a and 20b, and then control the charging and discharging of the capacitor 18.

FIG. 4a shows a typical output voltage 24 of the bridge rectifier 10 in response to an AC signal application from the power source 12 on the input side. It should be understood that, as mentioned above, the output voltage 24 is in the form of DC signals of different sizes. Figure 4a also shows a threshold level 26. Three operating modes are shown in Figure 4a. In mode 1, the output voltage 24 of the bridge rectifier is greater than the threshold level 26 and continues to rise; in mode 2, the output voltage 24 of the bridge rectifier is higher than the threshold level 26 but gradually decreases; while in mode 3, the bridge rectifier The output voltage 24 of the rectifier is lower than the threshold level 26.

FIG. 4a also shows the output voltage 30 of the electrical device of FIG. The control configuration 22 is used to control the positions of the switches 20a and 20b, so that in mode 1, the output of the bridge rectifier 10 meets the load 28 (indicated by a resistor in FIG. 3), and the switch 20a is closed, so that the capacitance 18 starts charging. Switch 20b It is open in this mode, but the end result of the positions of the switches 20a and 20b is that the switch 20 is closed. Figure 5a shows an equivalent circuit operating in mode 1.

In mode 2, the output of the bridge rectifier 10 continues to meet the load 28, but the switches 20a and 20b are both turned off, so that the capacitor 18 remains in a charged state. Since the switches 20a and 20b are both off, the overall state of the switch 20 is open. Figure 5b shows an equivalent circuit operating in mode 2.

In mode 3, the switch 20b is closed, so that the discharge of the capacitor 18 satisfies the load 28. In this mode, the switch 20a is still open, but since the switch 20b is closed, the overall effect of the switch 20 is closed circuit as a whole. Figure 5c shows an equivalent circuit operating in mode 3.

The control configuration 22 continuously monitors the output voltage 24 of the bridge rectifier, determines whether the output voltage 24 of the bridge rectifier is rising or falling, and compares the output voltage 24 of the bridge rectifier with a predetermined output threshold level 26 to It is convenient to determine which of the three operation modes is appropriate, and control the switches 20a and 20b accordingly. However, assuming that the frequency and magnitude of the power supply voltage are stable, the periodic cycle of operation of the switches 20a and 20b may use other control strategies. In addition, as described below, when the power supply voltage varies, other control strategies can be used.

FIG. 4b shows the actual output voltage of the electrical device of FIG. 3 when tested with an AC input voltage of 110V (rms). The threshold level 26 is set to 48V in this example.

FIG. 6 a is a schematic diagram of supplying the applied input current to the electric conversion circuit of FIG. 3. It should be understood that the aforementioned input current includes a portion corresponding to the three modes defined above. In mode 1, the applied input current is high. This is shown in Figure 6a as a square wave. This is usually not the case, and will depend to some extent on the load 28 Nature. As mentioned earlier, in this mode, the switch 20a is closed, the capacitor 18 is charged, and the load 28 is powered. In mode 2, when the switches 20a and 20b are both turned off, the supply current is partially sinusoidal, reflecting the nature of the input voltage. In mode 3, when the switch 20b is closed, the load 28 can be satisfied from the discharge of the capacitor 18, and the current supplied is zero. Figure 6a is a theoretical representation of the input current, while Figure 6b shows the actual impact of harmonics on the input current in a test configuration.

By correctly confirming the duration of each mode, the rms input current value can be calculated. In one example, when the power supply is 110V (rms) and the load 28 is a 36Ω resistive load, the rms input current value can be calculated to be about 3.9A. The calculation or determination of the volt-ampere value and the average instantaneous power value enables the power factor to be calculated to be approximately 0.94. A circuit using these values was constructed and tested to confirm the correctness of the calculation with a measured power factor of 0.936. For the power factor value of 0.3 to 0.6 obtained by a general electric conversion circuit, the aforementioned power factor value shows a significant improvement. It should be emphasized that this device is not limited to the above-mentioned supply voltage. In contrast, the maximum supply voltage that can be applied by this device is limited only by the rating of the switching element used.

Figure 7 shows a comparison of three test results, each test result from a different circuit configuration, showing possible improvements in current harmonics compared to the device in Figure 1: Figure 7a shows the actual input current of the electrical device in Figure 1 As a result of testing for harmonics, the electric device of FIG. 1 has a smoothing capacitor 14 of 660 μF and a resistive load 28 of 36 Ω.

FIG. 7b shows the test results of the actual input current harmonics of the electrical device of FIG. 3. The electrical device of FIG. 3 has a 660 μF switched capacitor 18 and a 36 ohm resistive load 28. This figure shows the improvement in current harmonics and power factor using a switched capacitor compared to Figure 7a.

Fig. 7c shows a test result of actual input current harmonics of the electric device of Fig. 3 As a result, the electrical device of FIG. 3 has a 68 μF switched capacitor 18 and a 36 Ω resistive load 28. This figure shows the improvement in current harmonics and power factor using switched capacitor 18 with a smaller capacitance value compared to FIG. 7b.

For all test results shown in Figure 7, the load 28 is the same.

The advantage of the configuration of the present invention is that it can achieve a significant increase in power factor and can suppress the generation of current harmonics. These effects can be achieved without integrating the switch into the current supplied to the load 28. Therefore, the present invention has particular advantages when it is used in a medium or high power application where integration of switches may cause problems. Although the advantages of the present invention can be realized without integrating the switch into a power source, the present invention can still be used in combination with such a power source when necessary.

It should be understood that the selection of the threshold level 26 depends to some extent on the application of the present invention, but the threshold level 26 also affects the size of the capacitor 18. A higher threshold level 26 requires a larger-sized capacitor 18, while a lower threshold level 26 requires a smaller-sized capacitor 18.

FIG. 8 shows a modification of the circuit of FIG. 3. In the circuit shown in FIG. 8, a monitoring circuit 32 is used to monitor the power source 12, and the output of the monitoring circuit 32 is supplied to the control unit 22 and used to control the operation of the switch 20. By using this configuration, the threshold level 26 can be changed, for example, in response to a 12 change in the power source detected by the monitoring circuit 32. Therefore, this configuration allows the threshold level 26 to be dynamically controlled to control the operation of the device as a whole, such as maximizing the power factor or power flux. This configuration is a unique advantage when the load is not fixed and / or not purely resistive.

Although FIG. 8 shows that the monitoring circuit 32 is used to monitor the power source 12, it should be understood that it may additionally or also be able to monitor the output of the rectifier, and for the determination of the appropriate threshold level 26, and / or for switching 20 controls.

FIG. 9 shows a modification of the circuit of FIG. 8. In the configuration of FIG. 9, an inductor 34 or other energy storage device is connected to the capacitor 18, and a freewheeling diode 36 is connected across the capacitor 18 and connected in series with the inductor 34. The configuration of FIG. 9 operates in substantially the same manner as previously described. That is, in the mode 1, the output of the bridge rectifier 10 satisfies the load 28 (resistance 28 shown in FIG. 9), and the switch 20 a is closed so that the capacitor 18 is charged. In the embodiment of FIG. 9, this mode also stores energy in the inductor 34. The switch 20b is turned off in this mode. Figure 10a shows the equivalent circuit operation in mode 1. Mode 1 therefore stores energy in one or more energy storage devices.

In mode 2, the output of the bridge rectifier 10 continues to meet the load 28, but the switches 20a and 20b are both turned off so that the capacitor 18 remains in a charged state. In the embodiment of FIG. 9, in this mode, the energy of the inductor is partially or completely transferred to the capacitor. Figure 10b shows the equivalent circuit operation in mode 2.

In mode 3, the switch 20b is closed so that the capacitor 18 is discharged to satisfy the load 28. In the embodiment of FIG. 9, in addition to the energy from the capacitor, the stored energy from the inductor can also be used to supply the load. In this mode, the switch 20a remains open. Figure 10c shows the equivalent circuit operation in mode 3.

As shown in FIG. 11, the configuration of FIG. 9 may cause the trans-potential of the load 28 in mode 3 to exceed the spike potential of the AC power source. Alternatively, using an appropriately sized inductor 34, the energy transfer rate can be designed to have less energy in the storage element, resulting in a spike potential in mode 3 that is less than the spike potential of the alternating current.

The inventor believes that the configuration of FIG. 9 is particularly suitable for use with high frequency power sources, such as those used in aircraft, because higher frequencies allow smaller inductors to be used.

An electrical conversion circuit configuration according to another embodiment of the present invention is shown in FIG. 12. The circuit of FIG. 12 is similar to the circuit of FIG. 9, but the flywheel diode 36 shown in FIG. 9 is omitted and replaced by another switching device 38, which is also operated by the control configuration 22. The operation of the configuration of FIG. 12 is substantially the same as described above with reference to FIG. 9, except that the switch 38 is controlled by the control configuration 22 so as to be opened in mode 1 and closed in modes 2 and 3, so that approximately The above operates in the same manner as the flywheel diode 36 configured in FIG. 9.

An electrical conversion circuit configuration according to another embodiment of the present invention is shown in FIG. 13. In the configuration of FIG. 13, the DC-DC converter 40 is connected in parallel to the output 10 b of the rectifier 10 and is also connected in parallel to the switched capacitor line 16. The purpose of setting the DC-DC converter 40 is to assist the output voltage of the rectifier to be stable, so as to maintain the voltage output to the load 28 as a stable DC voltage. According to the topology of the DC-DC converter 40, the smooth DC output across the load may be greater than or less than the threshold level 26.

Figure 14 shows a comparison of the two test results, showing the possible improvement in the current harmonics of the device of Figure 13 compared to the device of Figure 1: Figure 14a shows the test results of the actual input current harmonics of the electrical device of Figure 1, Figure 1 The electric device has a 660 μF smoothing capacitor and a DC-DC converter connected to the output 10 b of the rectifier 10 and a load 28.

FIG. 14b shows the test results of the actual input current harmonics of the electrical device of FIG. 13. The electrical device of FIG. 13 has a 68 μF switched capacitor 18 and a load 28 that is the same as that of FIG. 14a. The DC-DC converter used for the test shown in FIG. 14a is the same as the DC-DC converter 40 in FIG. Figure 14b shows the improvement of current harmonics and power factor over Figure 14a.

The test loads 28 shown in FIG. 14 are all the same and are composed of a notebook computer running a Linux operating system while undergoing a rigorous stress test. Two tests The output of the DC-DC converter used is set to 19V.

Although the circuits shown in FIGS. 9, 12, and 13 all use the modification shown in FIG. 8, it should be understood that the embodiments based on the changes including FIG. 9, FIG. 12, and FIG. 13 and the circuit based on FIG. It is possible.

Although specific embodiments of the present invention have been described in the foregoing with reference to the accompanying drawings, it should be understood that a wide range of modifications or changes can be made without departing from the scope defined by the scope of the patent application accompanying the present invention. category.

Thanks to the development of the subject matter related to this application, especially the embodiments shown in Figs. 8 to 13, and the testing of the present invention were all performed by Fairford Electronics, Ivybridge, UK Friendly assistance and collaborative work.

Claims (13)

An electric conversion device includes: a bridge rectifier having an input side and an output side; a switched capacitor line connected in parallel to the output side of the bridge rectifier; the switched capacitor line includes a capacitor connected in series with each other and a A switch that controls the electrical contact between the output side of the bridge rectifier and one end of the capacitor, so that the switch controls the charging and discharging of the capacitor; and a control configuration to control the operation of the switch; The switch is a two-way switch. The operation of the control configuration is such that when one of the bridge rectifiers' output voltage is above a threshold level and continues to rise, the switch is closed to charge the capacitor and the bridge rectifier. The output voltage meets a load; when the output voltage of the bridge rectifier is higher than the threshold level and gradually decreases, the switch is turned off to insulate the capacitor from the load, and the output voltage of the bridge rectifier The load is still satisfied; and when the output voltage of the bridge rectifier is lower than the threshold level, the switch is closed to discharge the capacitor The full load. The electric conversion device according to item 1 of the scope of patent application, wherein the threshold level is fixed. The electric conversion device described in item 1 of the scope of patent application, wherein the threshold level is changed. The electrical conversion device described in item 3 of the scope of patent application, further includes a monitoring configuration for monitoring a power supply to the input side and / or an output on the output side, wherein the threshold level is to be monitored. Configuration operations are dynamically controlled. The electric conversion device described in item 1 of the patent application scope further includes an additional energy storage element arranged in series with the capacitor. The electric conversion device described in item 5 of the patent application scope further includes a flywheel diode connected in series to the energy storage element. The electric conversion device according to item 5 of the patent application scope, wherein the energy storage element includes an inductor. The electric conversion device described in the first item of the patent application scope further includes a DC-to-DC converter to provide a stable DC output waveform. The electric conversion device according to item 1 of the patent application scope, wherein the bidirectional switch includes a pair of unidirectional switches arranged in parallel and opposite directions. The electrical conversion device according to item 9 of the scope of the patent application, wherein each of the unidirectional switches includes a suitable switching device such as, but not limited to, a metal oxide semiconductor field effect transistor (MOSFET) or an insulated gate bipolar Transistor (IGBT). An electrical conversion method includes providing a switched capacitor line connected in parallel to one output side of a bridge rectifier. The switched capacitor line includes a capacitor connected in series with each other and a switch. The switch controls the output side of the bridge rectifier and The electrical contact between one end of the capacitor enables the switch to control the charging and discharging of the capacitor. The switch includes a bidirectional switch and its operation is such that when one of the bridge rectifiers has an output voltage above a threshold level During a quasi-continuous rising period, the switch is closed to charge the capacitor and the output voltage of the bridge rectifier meets a load; when the output voltage of the bridge rectifier is higher than the threshold level and gradually decreases, the The switch is disconnected to isolate the capacitor from the load, and the output voltage of the bridge rectifier still meets the load; and when the output voltage of the bridge rectifier is below the threshold level, the switch is closed to The discharge of the capacitor satisfies the load. The electrical conversion method described in item 11 of the scope of the patent application further includes measurement of AC input and / or DC output to dynamically generate the threshold level for controlling the switch. The electric conversion method according to item 11 of the scope of the patent application, wherein the switched capacitor line and the bridge rectifier form a part of the electric conversion device according to any one of the scope of patent applications 1 to 10.